Our long-term goal is to characterize functionally and morphologically the chemosensors of the nervous system concerned in the homeostasis of brainstem fnctions. Specific objectives of this project are: (1) to determine the central feedback source in the respiratory regulation of alveolar CO2 tension; (2) to identify the emetic receptor element of the area postrema in the medulla oblongata; (3) to elucidate the chemosensory mechanism in the nodose ganglion of the va us nerve. Each chemosensor will be probed in three ways desi ned to (a) delineate its reflex motor characteristics, (b) obtain access to its discrete site of chemosensitivity, and (c) control its sensed environment. Acute experiments are performed in unanesthetized decerebrate cats. Chronic experiments are performed in cats subjected to sterile operative procedures and maintained under close surveillance. Techniques to be employed include surgical and chemical ablations, cerebrospinal fluid perfusion, cross-circulation, radioautography and electrical activation and recording of neural discharges. Emphasis will be placed on effects of drugs upon CO2 regulation dynamics, on vomiting in narcotic addition, and on drug modulation of sensory nerve input to the central nervous system.